Guitar Roller String Trees String Tree Guide Retainer Replacement Guitar Parts for Electric Guitar Accessory Set (Chrome .10Pcs) The rollers lessen the stress on your strings which allows the guitar to stay in tune longer. This also prevents wear and tear on the strings which results in longer string life. Base is about 6mm (1/4") wide x 11.5mm (7/16") long Total height including roller is about 12mm